Hitherto, cemented carbide (WC—Co alloy or the like) obtained by sintering tungsten carbide powder with cobalt, nickel, or the like has been widely used in materials required to exhibit wear resistance, strength, and heat resistance for cutting tools, molds, heat resistant and wear resistant parts. The oxidation of this cemented carbide rapidly proceeds when it is used in a high temperature state of 600° C. or higher in the atmospheric air, and this cemented carbide is necessarily used at a temperature lower than this. However, cutting and mold machining at a high temperature state are increasingly required with the progress of machining technology, and a hard material usable at a higher temperature is demanded.
On the other hand, tungsten is a rare metal having country risk since the tungsten mine which is the raw material for tungsten carbide is unevenly distributed in some areas. For this reason, a cermet obtained by sintering a titanium carbide powder or a titanium carbonitride powder with cobalt, nickel, or the like is used instead of tungsten carbide. Cermet exhibits higher hardness and superior oxidation resistance as compared to cemented carbide.
However, cobalt and nickel are also rare metals of which the depletion as a resource is concerned. In addition, cobalt is designated as Class 1 Designated Chemical Substance in PRTR Law and Class 2 Specified Chemical Substance in Occupational Safety and Health Law, and it is thus not desirable to use cobalt from the viewpoint of cost and environmental convergence. From the facts described above, it is desired to develop inexpensive materials for tools which have resources to be stably supplied and do not contain a rare metal. As one measure to cope with the rare metal, a cemented carbide having a binder phase composed of one kind or two kinds between Fe and Al instead of cobalt is known (for example, Patent Literature 1). A hard material which does not contain a rare metal is obtained when the binder phase of cermet having titanium carbide (TiC) or titanium carbonitride (TiCN) in a hard phase is changed from cobalt or nickel to an intermetallic compound such as iron aluminide.
In the manufacturing methods of a composite material having iron aluminide as a binder phase, there is a method in which Fe, Al, and hard particles are mixed and Fe and Al are reacted at the time of sintering to produce FeAl, but it is difficult to increase the transverse rupture strength since it is difficult to refine crystal grains (for example, Patent Literatures 1 and 2). In addition, in a manufacturing method of a composite material in which an FeAl powder (pre-alloy) obtained by previously synthesizing Fe and Al by combustion synthesis or the like and pulverizing the synthesized substance and hard particles are mixed and pulverized together with additives and then sintered, the hardness of the composite material is improved by increasing the mixing and pulverization time (for example, Patent Literature 3).
However, the grain refinement proceeds and, at the same time, oxidation of the mixed powder also proceeds when the mixing and pulverization time is increased. As a result, although material properties such as hardness are improved, there is a problem that FeAl and oxygen adsorbed on the mixed powder surface are converted into Fe and Al2O3 through the reaction represented by the following chemical reaction formula (1) and the oxidation resistance thus decreases as the oxidized FeAl mixed powder is exposed to a high temperature at the time of sintering.4FeAl+3O2→4Fe+2Al2O3   (1)
In addition, in the manufacturing method of a composite material in which a preform is formed from hard particles and FeAl is infiltrated into the preform, there is a problem that it is difficult to densify the composite material and the hardness and transverse rupture strength of the composite material decrease.